There are in total, 4 measure entries. Notice
that for each "+" there is a corresponding "-."

Because a measure of relative size is simply a
measure of difference, we could've ascertained
a priori that the change in size would sum to
0 by observing that as a rule, the sum of
all differences between all numerical
measurements always equals zero:

"A new scientific truth does not triumph by convincing its
opponents and making them see the light, but rather because
its opponents eventually die, and a new generation grows
up that is familiar with the idea from the beginning."

Max Plank - Nobel physicist

"The smallest minority on earth is the individual.
Those who deny individual rights cannot claim
to be defenders of minorities." Ayn Rand